The present invention relates to systems and methods for metal plating. More particularly, the invention relates to techniques for controlling the structure and properties of electroplated and electroless plated metals.
Metal plating of articles or base substrates is a common industrial practice. A metal layer may be coated or plated onto the surface of an article, for example, for decoration, reflection of light, protection against corrosion, or increased wearing quality. Articles or base substrates, which are made of metal or non-metallic material, may be plated with suitable coating metals using techniques such as electroplating, electroless plating, metal spraying, hot dip galvanizing, vacuum metallization or other available processes. Plating by electrolysis, or electroplating, is a commonly used technique for metal plating because it permits the control of the thickness of the plating. Cadmium, zinc, silver, gold, tin, copper, nickel, and chromium are commonly used plating/coating metals. In immersion or electroless plating, some metals are directly precipitated, without the application of externally applied sources of electricity, from chemical solutions onto the surface of the substrates. The silvering of mirrors is a type of plating in which silver is precipitated chemically on glass. Any of the common metals and some nonmetals, e.g., plastics, with suitably prepared (e.g., etched) surfaces can be used as the article or base substrate material.
A coated or plated metal layer may have structural properties (e.g., grain size, grain orientation, density, porosity, etc.) that are different from other forms of the metal (e.g., bulk material or sprayed materials) because of their different manner of preparation. The structural properties of the coated or plated metal layer, depending on the method of preparation, can in some instances be advantageous or disadvantageous for certain applications. For example, porosity can be detrimental with respect to corrosion, machined finish, strength, macro hardness and wear characteristics. Conversely, porosity can be advantageous with respect to lubrication (porosity acts as reservoir for lubricants), increasing thermal barrier properties, reducing stress levels and increasing thickness limitations, increasing shock resisting properties, abradability in clearance control coatings, applications in nucleate boiling, etc. Thus, it is desirable to control the structural properties of a coated or plated metal layer according to the desired application properties of the metal layer.
Electro and electroless plating operations using gold and copper deposits have a wide range of applications, from PCBs (printed circuit boards) to automotives and jewelry. However, existing gold-plating technologies have several shortcomings, including higher than desired electrical resistivity, susceptibility to corrosion and significantly higher plating thicknesses of the gold deposit than is intrinsically required, which drives up the cost of the plating process.
Consideration is now being given to improving electro and electroless plating systems and methods. Attention is particularly being directed to techniques for controlling the structural properties of electroplated and electroless plated metals, with particular emphasis on reducing the porosity of the deposit. A principal feature of the present invention is the in-situ annealing of the deposit by controlled heating of the deposit during its growth.